Digital Watercolour NPR Techniques of Allan Casas is a step by step tutorial in creating a non-photo realistic rendering. The tutorial will start with the introduction of the technique and will then go straight ahead with some exercises with two styles in the technique.
The technique is just a base of what you will still achieve if you will learn to incorporate your own style and influences in this art of presentation.

The book also includes a complete project files with sample projects and textures needed for the tutorial. There are also five bonus exercises at the end of the book to further enhance what you have learned at the beginning.